Use of time and space

Abstract

Fishes use the dimensions of time and space in many ways. The individuals of some species spend all their lives close to where they were spawned. In other species, individuals make long migrations covering hundreds or thousands of kilometers. There are species that have vertical migrations, with individuals moving up and down in the water column. The ecological significance of many of these patterns of movement is unexplained. The reproductive advantage gained is not always obvious. In several species, for example the European trout, Salmo trutta, some populations migrate covering long distances yet other populations remain resident in one area and show only restricted movements. A single watershed frequently holds both migratory and resident populations of S. trutta. Why is it advantageous for some individual trout to migrate, while other coexisting individuals remain as residents in the watershed?